Nowadays, humidity measurement has become an essential tool in environmental monitoring for HVAC (heating, ventilation, and air conditioning), communications base stations, building security, etc.
Currently, commercially available electronic devices for humidity measurement used in environmental monitoring achieve the measurement, conversion and transmission of humidity by activating a humidity-sensitive element. Generally, the humidity-sensitive element may be capacitive, or resistive. In resistive humidity-sensitive elements, the effect of humidity is the change in the electrical resistance of a material. The electrical resistance can vary dramatically, and is in a logarithmic relationship with the humidity to be measured, causing inconvenience in measurement and conversion, and limited range of measurement. The measurement range for relative humidity is normally between 20% RH and 95% RH with an accuracy of about 5%. In capacitive humidity-sensitive elements, the effect of humidity is the change in the electrical capacitance of a material, which is in a substantially linear relationship with the humidity to be measured. The measurement range can be 0% RH to 100% RH, hence the full range, with an accuracy of about 1% to 3%. As a result, humidity-sensitive capacitors are generally used for industrial use, e.g., as humidity-sensitive elements, while humidity-sensitive resistors are generally used for commercial use, e.g., as hygrometers.
However, both types of humidity-sensitive elements have the problem of high-temperature drift, and may have reduced accuracy due to condensation or dust, or even break down or be damaged in severe conditions.